Lined shaped explosive charge and liner therefor



Feb. 19, 1963 B. M. CALDWELL LINED SHAPED EXPLOSIVE CHARGE AND LINER THEREFOR Filed July 14, 1958 INVENTOR F ig.l

Fig.2

BY m h.

ATTORNEY iiniteti tates This invention relates to lined shaped explosive charges, and to liners therefor. Although of general utility in the shaped explosive charge field, the invention is especially useful in connection with the perforation of oil, gas, or water wells and the like.

It is common practice in completing oil Wells to lower into the cased well to the level of the earth formation of interest a well perforating apparatus, including one or more shaped explosive charge perforating units positioned to direct perforating jets through the casing and into the earth formation for the purpose of opening up the formation to the well bore, and thereafter to fire the perforating units. In the usual perforating unit, the cavity of the shaped explosive charge is lined with a solid metal liner, usually a copper liner. Upon firing the device, a high-velocity jet of tremendous energy is formed from portions of the liner and this jet is projected into the formation to form a perforation therein. In addition to providing the metal portion of the jet, solid copper or other solid metal liners also form what is known as a carrot or slug that often follows the jet into the perforation. Such slug may block the perforation and thus prevent or seriously diminish the fiow of fluid from the formation through the perforation and into the well, thereby defeating the purposes of the perforating operation.

Much research has been done looking toward minimixing the plugging of perforations by the carrot and some solutions to the problem have been proposed that have been more or less successful. One line of research has been directed to the use of mechanical means in association with the charge unit or perforating apparatus for preventing projection of the carrot into the perforation. Such mechanical means do not eliminate formation of the carrot but attempt to intercept the carrot in its trajectory and prevent the carrot from entering the perforation. Another line of research has attempted to minimize the size of the carrot or preclude its formation by modification of components of the shaped charge unit. However, the latter line of research has encountered difficulties in that perforating efliciency is lost as carrot size is diminished.

Therefore, an object of the invention is to provide a shaped explosive charge unit and a liner therefor having excellent perforating efiiciency and exhibiting the property of producing no carrot when fired.

Another object is to provide a liner for the cavity of a shaped explosive charge that facilitates manufacture of the explosive unit of which it is a component.

Still another object of the invention is to provide such a liner that is physically strong enough to withstand rough handling encountered in its assembly into the shaped explosive charge unit and in shipment of such units, yet has internal physical structure rendering it porous and relatively weak in tensile strength.

A further object is to provide in such a liner a geo metrical configuration that contributes to its carrot-free nature.

Still further aims, objects and advantages of the invention will appear in or be evident from the following description.

In general, the invention includes a liner for the cavity 3,677,834 Patented Feb. 19, 1963 of a shaped explosive charge, the liner being in the desired shape, such as in the form of a cup-shaped shell, the liner being comprised of a multiplicity of small, solid metal spheres arranged in loosely packed formation, the spheres being joined together, as by welding, substantially only at their areas of mutual contact. The loosely packed arrangement of the spheres provides a porous structure having voids between the spheres. The spheres are of substantially uniform diameter, and the diameter of the spheres may range from about 3 microns to about 50 microns in various embodiments of the invention.

The spheres that are used for making the liner may be of copper, bronze or other solid metal or alloy and they may be coated with a thin film of a metal or alloy having a lower melting point which, upon heating, will melt and thereafter, upon cooling, will solidify to bond the spheres together at their areas or points of mutual contact.

In one form of the invention the spheres are of copper coated with a thin layer of tin, which may be applied thereto by electrodeposition. Other substances such as adhesives may be used to cause the spheres to adhere to one another at their points of contact without filling the voids or spaces between the spheres. The structure thus formed has relatively high compressive strength an low tensile strength.

. Instead of using metal spheres coated with a film of another metal having a melting point lower than the melting point of the metal of the spheres and capable of alloying therewith, uncoated metal spheres may be used. Where, for instance, uncoated copper spheres are employed, such spheres are caused to adhere to each other merely by heating the spheres in a mold to a temperature slightly below the melting point of the copper and holding them at such temperature for a short time; although under such treatment the spheres do not lose their original shape, they do become sintered together at their points of contact.

A liner in accordance with another embodiment of the invention may be a composite structure in which a thin shell of solid copper, for example, or other suitable metal may be adherently coated on the back or convex side with a layer composed of a multiplicity of spheres in loosely packed arrangement, the spheres being joined together, in the manner disclosed herein, substantially only at their areas of mutual contact.

Shaped explosive charges and charge units employing the liners of the invention are of course contemplated.

The present invention also provides a special geometrical configuration of cavity liner formed of small spheres that enhances the degree of disintegration of the liner when a charge including the liner is detonated. Tests have shown that improved results are obtained where a liner formed from spheres in accordance with the invention and having a generally cup-shaped shell having thin side walls is provided with a substantially cylindrical boss integral with the shell and projecting coaxially and rearwardly from the apex of the shell. Such cylindrical boss may have a diameter of from about oneeighth to about three-eighths of the diameter of the base of the shell. The thickness in the axial direction of the shell including the boss may be from about one-and-onehalf times to about three times the average thickness of the side walls of the shell. Although the boss is preferably cylindrical, it may take other geometrical forms such as to provide an axial zone of the liner having sharply and substantially increased thickness with respect to the thickness of the forwardly extending wall sections.

Whereas, it has been found that the provision of a boss at the apex of the liner enhances the perforating effect that is obtainable, it will be understood that the invention is not restricted to such geometrical configuration of liner but that the advantages of the invention are also realized in liners of other configurations, such as those having uniform or slightly varying wall thickness.

In the drawings:

FIG. 1 is an axial sectional view of a shaped explosive charge well perforating unit in accordance with the invention;

FIG. 2 is an isometric view of the cavity liner of the unit shown in FIG. 1;

FIG. 3 is an axial sectional view of the cavity liner;

FIG. 4 is a vertical sectional view of a mold used for making liners; and

FIG. 5 is a vertical sectional view of another form of cavity liner in accordance with the invention.

Referring to the drawings, particularly to FIG. 1 thereof, the shaped explosive charge well perforating unit shown has a casing 10, which may be a zinc-base alloy die-casting, the casing being a body of revolution about a longitudinal axis. The casing is generally cup-shaped and is open at the forward end 11. The casing has a charge-receiving hollow portion 12, the side walls of Which curve convergingly inwardly toward the generally rounded bottom 13 of the hollow. The walls of the casing have a gradually increasing thickness from front to rear. A generally cylindrical axial extension 14 projects from the back of the casing and has a detonating fuse receiving hole 15 extending transversely therethrough. A flexible rubber jacket 16 is fitted over the casing and covers the lateral and rearward exterior faces of the casing.

A booster cup 17 is fitted into an axial cylindrical recess 18 opening into the bottom of the hollow 12. The booster cup contains a charge of compressed booster material 19 which may be pure RDX, tetryl, or the like.

The main explosive charge, designated by the reference numeral 20, is received within the bottom section of the cup-shaped hollow 12. The main explosive charge may be of desensitized RDX or other conventional high explosive.

v A liner 21 lines the walls of the cavity formed in the front face of the main explosive charge.

Referring to FIGS. 2 and 3 showing the cavity liner 21 in isometric view and axial sectional view, respec tively, the liner is in the form of a cup-shaped shell having a circular base 23. The side walls of the shell have a cylindrical forward section 24 the periphery of which engages the interior of the casing, as shown in FIG. 1, to provide a relatively firm seat for the liner against the side walls of the casing. The walls of the liner c0n verge symmetrically to the rear and merge into the generally rounded apex portion 25. Projecting rearwardly from the apex of the liner is a generally cylindrical boss 26 formed integrally with the liner. It will be seen that the thickness of the walls of the liner from the base rearwar'clly to the boss gradually increases and that the thickness of the liner measured from the inner surface to the rear face of the boss is approximately twice the mean thickness of the side walls. The diameter of the boss is approximately one-fourth the diameter of the base of the liner. The liner is generally conical or paraboloidal in shape but it may take other forms, such as hemispherical.

The manufacture of the liner of FIGS. 1 to 3 will be described by way of example with reference to FIG. 4. The liner mold shown in FIG. 4 is formed in two sections. The lower section has a base 27 with an upstanding generally conical projection 28 conforming to the front face of the liner. The upper section 29 of the mold has a complementary recess 30 conforming to the rearward face of the liner and spaced from the projec tion 28 to provide a cavity 31 having the form of the liner to be molded therein. The upper section 29 of the V mold has a sprue hole 32 communicating with the cavity 31 and having the shape of the boss 26 of the cavity liner 2.1.

The mold sections are assembled as shown in FIG. 4 and the cavity 31 and sprue hole 32 are filled with the small uniform metallic spheres which will compose the finished liner. The mold is vibrated, either mechanically or by hand, during the filling operation so that the spheres assume a normal loosely packed arrangement in the mold cavity 31. It is to be noted that the spheres are allowed to assume their positions in the mold cavity by the action of gravity and light vibration and are subjected to no additional pressure.

The mold as thus filled with small spheres is placed in a furnace and brought up to a temperature at which the spheres are welded together only at their areas of mutual contact. The spheres may have a thin coating of welding material thereon, if desired. Such welding material preferably has a lower melting point than the melting point of the spheres themselves so that fusion and welding can take place without melting the spheres. Thus the spaces between the spheres are kept substantially open.

After the furnacing operation, the mold and its contents are removed and allowed to cool. Then the sections of the mold are taken apart and the finished liner is removed.

It has been found advantageous to use spheres of copper, each having a diameter of 5 microns. The spheres are coated with a film of tin, the weight of the tin coating to the weight of the copper spheres being in the ratio of approximately 5 to 95. In the furnacing operation, the tin melts and Welds the spheres together by alloying with the spheres to form a copper-tin bronze.

In FIG. 5 there is shown a modified form of cavity liner designated by the reference numeral 33. The liner 33 may have the same general shape as the liner 21 of FIGS. 1 to 3. However, instead of being composed entirely of small spheres of metal, the front section of the liner 33 consists of a thin solid layer of metal 34 backed up by an adherent layer 35 formed from small metal spheres, such as copper for example, as described hereinbefore. U

The liner 33 may be made in the mold shown in FIG. 4- by simply placing the layer 34, of solid metal preformed to the desired contour, over the projection 28 before closing the mold sections. Thereafter, the mold is filled with metal spheres as described hereinbefore. The spheres occupy the space in the cavity 31 remaining between the solid metal liner section 34 and the top of the mold cavity 31.

Upon furnacing, the spheres are welded together and those spheres adjacent to the rear portion of the solid preform 34 are welded to the preform at the points of contact therewith.

The particular liner shown by Way of example in FIG. 3' has the form of a generally cup-shaped shell. It has approximately the outline of a parabola in cross-section and has a base diameter of 1.69" and a height measured from the plane of the base 23 to the rear face of the boss 26 of 1.00". Wallthickness are as follows:

Inches Point A 0.06 .Point B 0.0-7 Point C 0.07 Point D 0.09 Point E 0.16

The diameter of the boss is 0.400. The spheres forming the liner are each approximately 5 mircons in diameter and are coated each with a thin film of tin. The spheres are of copper.

The liner shown in FIG. 5 has the same outside dimensions as the liner shown in FIG. 3. However, the solid insert 34 may be of copper having a thickness of 0.015". The thickness of the layer 35 of copper or bronze spheres is reduced by an amount equal to the thickness of the insert 34.

When assembled into the well perforating unit shown in FIG. 1, the liner 21 of FIG. 3 is backed up by main charge 24 consisting of 19 grams of waxed granular RDX.

When such a charge is fired into a target simulating a section of cased oil well, a deep perforation is formed through the well casing and in the simulated earth formation therebeyond. No carrot is formed and, of course, none is found in the perforation.

When a shaped charge unit having a liner in accordance with the present invention is fired into a foam tank and the liner particles are recovered from the tank, it is seen that the liner is reduced substantially entirely to a powder resembling in size the original sperical particles from which the liner has been fabricated. No carrot is found in the recovered liner material.

The foam tank referred to is a wide, open-top tank hav ing about four feet of water in the bottom with a layer of detergent foam four to six feet deep floating on the water. The jet from the charge unit is fired vertically downwardly through the foam and the energy of the jet particles, including the carrot if any, is absorbed in the foam layer and in the water. The particles are thus recovered in substantially undamaged condition.

X-ray photographs of exploding shaped charges including liners in accordance with the invention have shown that no carrot is formed.

The liners of the present invention are characterized by being formed from small solid metal spheres of substantially uniform diameter arranged in loosely packed orientation and joined together only at their points of mutual contact to provide voids between the spheres.

The provision of voids in the liner is found to result in improved penetration, for when the voids are filled by tin or lead that has been melted into the porous liner structure of the invention, the penetration achieved is greatly reduced. Also, the porous liner of the invention is much easier to assemble into a complete charge unit that is a conventional solid copper liner. When the liner is pressed into the explosive material, air that is trapped between the liner and the explosive escapes through the pores of the liner and there is no tendency for the liner to become unseated due to the force exerted by compressed air trapped between the liner and the explosive. Moreover, the porous and relatively rough rear surface of the liner provides a surface having tooth to which the explosive material bonds with considerable tenacity, thus eliminating the necessity of securing the liner in assembled position by means of an adhesive composition.

The employment of metal spheres of substantially uniform size produces a liner construction having greater physical strength than one made from particles of irregular shape.

From the foregoing description, numerous variations and modifications will occur to those skilled in the art of shaped charge explosives without departing from the invention. The liners of the invention may be incorporated in shaped charge units utilizing the so-called barrier principle wherein a body of metal is embedded in the explosive material between the point of detonation and the liner. It is also contemplated that linear and annular shaped charge devices may include the liners of the invention.

Iclaim:

l. A shaped explosive charge unit comprising:

(a) a casing;

(b) a shaped explosive charge in said casing, said charge having an outwardly flaring cavity in the front face thereof;

(0) a liner lining the walls of said cavity, said liner comprising a multiplicity of solid metal particles of an alloy containing copper as the major constituent, said particles being of,- a substantially uniform size and each having a diameter greater than about 3 microns and smaller than about 50 microns and many times smaller than the thickness of said liner, each of said particles having a thin, adherent coating of a metal alloy containing tin which has a melting point below that of said copper alloy, each one of said particles contacting adjacent particles only at small areas spaced apart on the surface of the particle to define interconnected voids between said particles, weld means comprising said coatings of tin-containing alloy for joining said particles together only at said areas of contact to form a rigid, porous, frangible structure Weak in tensile strength; and

(d) means for detonating said explosive charge.

2. A shaped explosive charge unit comprising:

(a) a casing:

(11) a shaped explosive charge in said casing, said charge having an outwardly flaring cavity in the front face thereof;

(a) a liner lining the walls of said cavity, said liner comprising a multiplicity of solid metal particles of an alloy containing copper as the major constituent, said particles being of a substantially uniform size and each having a diameter greater than about 3 microns and smaller than about 50 microns and many times smaller than the thickness of said liner, each one of said particles contacting adjacent particles only at small areas spaced apart on the surface of the particle to define interconnected voids between said particles, weld means comprising a thin film of metal alloy other than the copper-containing alloy of said particles, said metal alloy having a melting point substantially below the melting point of the copper-containing alloy of said particles, for joining said particles together only at said areas of contact to form a rigid, porous, frangible structure weak in tensile strength; and

(d) means for detonating said explosive charge.

3. A shaped explosive charge unit comprising:

(a) acasing;

(b) a shaped explosive charge in said casing, said charge having an outwardly flaring, generally cupshaped cavity in the front face thereof;

(6) a liner in the form of a generally cup-shaped shell having an open base lining the walls of said cavity, said liner having thin side walls and a substantially cylindrical boss integral with said shell and projecting coaxially and rearwardly from the apex of said shell, said cylindrical boss having a diameter of from about one-eighth to about three-eighths of the diameter of the base of said shell and the thickness of said shell and boss in the axial direction being from about one and one-half times to about three times the mean thickness of the side walls of said shell, said shell and said boss consisting essentially of a multiplicity of solid metal particles of an alloy containing copper as the major constituent, said particles being of a substantially uniform size and each having a diameter greater than about 3 microns and smaller than about 50 microns, each one of said particles contacting adjacent particles only at small areas spaced apart on the surface of the particle to define interconnected voids between said particles, weld means for joining said particles together only at said areas of contact to form a rigid, porous, frangible structure weak in tensile strength; and

(d) means for detonating said explosive charge.

4. A shaped explosive charge unit comprising:

(a) a casing;

(b) a shaped explosive charge in said casing, said charge having an outwardly flaring, generally cupshaped cavity in the front face thereof;

'(c) a liner in the form of a generally cup-shaped shell having an open base lining the walls of said cavity, said liner having thin side walls and a sub- 8 l stantially cylindrical boss integral with said shell References Cited in the file of this patent I and projecting coaxially and rearwardly from the UNITED STATES PATENTS apex of said shell, said shell and said boss consisting essentially of a multiplicity of solid metal par- Lawson ticles of an alloy containing copper as the major 5 2529325 Sweetman 1953 constituent, said particles being of a substantially Church et 1954 uniform size and each having a diameter greater 27963333 Sweetman June 1957 than about 3 microns and smaller than about 50 FOREIGN PATENTS microns, each one of said particles contacting adja- 574 132 Gmat Britain Dec 21 5 cent particles only at small areas spaced apart on 10 1379O6 Australia 1950 t the surface of the particle to define interconnected 9809O3 France Jan 195-1 yoids between said particles, weld means for join- 0 France t II? 3 mg said particles together only at said areas of con- OTHER REFERENCES tact to form a rigid, porous, frangible structure Weak in tensile strength; and 15 Materials Handbook, 8th edition, by Brady, published ((1) means fior detonating said explosive charge. by McGraw-Hill Book (30., p. 426. 

1. A SHAPED EXPLOSIVE CHARGE UNIT COMPRISING: (A) A CASING; (B) A SHAPED EXPLOSIVE CHARGE IN SAID CASING, SAID CHARGE HAVING AN OUTWARDLY FLARING CAVITY IN THE FRONT FACE THEREOF; (C) A LINER LINING THE WALLS OF SAID CAVITY, SAID LINER COMPRISING A MULTIPLICITY OF SOLID METAL PARTICLES OF AN ALLOY CONTAINING COPPER AS THE MAJOR CONSTITUENT, SAID PARTICLES BEING OF A SUBSTANTIALLY UNIFORM SIZE AND EACH HAVING A DIAMETER GREATER THAN ABOUT 3 MICRONS AND SMALLER THAN ABOUT 50 MICRONS AND MANY TIMES SMALLER THAN THE THICKNESS OF SAID LINER, EACH OF SAID PARTICLES HAVING A THIN, ADHERENT COAT- 